High performance and low cost are the two main drivers for large scale applicability of semiconductor electronics and sensors. Thus, the challange facing the semiconductor industry is to reduce production cost while maintaining or improving device performance. In many thin film semiconductor applications, including sensor and other devices, a major technical difficulty is the lack of a suitable epitaxial template for the growth of well-oriented films. Favorable device characteristics are generally better defined and more pronounced in well-oriented (i.e., nearly single-crystalline) thin films, but conventional epitaxial film-growth techniques require single crystal templates that are either expensive or of limited availability or both.
Ion-beam-assisted deposition (IBAD) texturing has been widely used in the preparation of high temperature superconducting films in coated conductors (see, e.g., Iijima et al., U.S. Pat. No. 5,650,378 and Arendt et al., U.S. Pat. No. 5,872,080). IBAD texturing can produce nearly single-crystalline films with crystallographic properties approaching those of conventional epitaxial thin films by using an off-normal ion beam to establish a preferred orientation for film growth on a non-single-crystalline (i.e., amorphous or polycrystalline) substrate. Once established, this IBAD layer serves as a biaxially-oriented template for the epitaxial growth of subsequent layers.
In photovoltaic applications, both minority carrier lifetime and majority carrier mobility are important parameters; the short circuit current is strongly dependent on minority carrier lifetime whereas fill factor and photovoltaixc yield are dominated by majority carrier mobility. However, for thin film transistor (TFT) applications, such as metal oxide semiconductor field effect transitor (MOSFET), the majority carrier mobility is the most important parameter.
Grain boundaries in polycrystalline semiconductor films can result in local lattice distortions and dangling bonds. Such structural defects and any associated impurity segregations can modify the energy band structure in the vicinity of the grain boundary, with implications for minority carrier recombination and majority carrier transport across the boundary plane. It has been shown both theoretically and experimentally that better grain alig/ment and larger grain size lead to overall enhancement of carrier mobility.
Photovoltaic energy conversion efficiency (measured under the global AM1.5 spectrum at a cell temperature of 25° C.) for solar cells that use single crystalline silicon can approach 24%, whereas solar cells based on amorphous silicon structures seldom surpass 8% efficiency. Some prior efforts have been directed to converting amorphous silicon to microcrystalline or polycrystalline silicon (See, e.g., U.S. Pat. No. 5,456,763 or U.S. Pat. No. 5,714,404). Direct deposition of a well-oriented semiconductor such as silicon would be desirable. Thus, a new materials technology that combines the functionality of non-single-crystalline substrates with the microstuctural order and associated enhanced electrical characteristics of well-oriented films (an important aspect of conventional silicon on insulator (SOI) and wafer bonding technologies) would be highly desirable.